What is a MERV Rating?

The MERV rating system was initially created by ASHRAE in 1987. The purpose of the Standard is designed to determine the following attributes of air filters:

Particle removal capability

Resistance to airflow

Expected operating life

How is an Air Cleaner’s MERV Rating Determined? Air cleaners are given MERV ratings based on the results of a series of tests. Simply put, the process works as follows:

Test particles are introduced into the air of the testing area. These particles fall into one of twelve categories, based on size. The smallest category contains particles ranging from .3 to .4 micrometers (also known as “microns”). The largest includes particles from 7 to 10 micrometers. The air is then passed through the filter being tested. The density of particles in the air is measured before and after the air passes through the filter to determine how effective the filter is at removing pollutants in each size category. After this is done, the process is repeated five more times so that there are ultimately six measurements for each of the twelve categories. The MERV number is assigned based on the worst result. Hence the “minimum” in “Minimum Efficiency Reporting Value.”

Conclusion The MERV rating system is a helpful way to describe the capabilities of different large air cleaners. It is determined through rigorous testing and it gives the worst-case performance of the filter, so the MERV number is not inflated. No one should forget to consider MERV ratings when shopping for such cleaners.

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